Wheel-brake cylinder or the like



United States Patent [72] Inventors Walter Fuchs Bad Homburg, Vonder Hohe, Erich Runge, Frankfurt, am Main, Juan Belart and Gert Schrader, Walldorf, Hessen,

[54] WHEEL-BRAKE CYLINDER OR THE LIKE 6 Claims, 3 Drawing Figs.

[52] U.S. Cl 92/165, 92/75: 277/57 [51] Int. Cl. Fl6j 11/04, Fl6j 15/44 [50] Field ofSearch 92/165,

[56] References Cited UNITED STATES PATENTS 8/1928 Farmer 92/165X 1,991,077 2/1935 Brittain 277/56 2,018,754 10/1935 White 188/79.5 2,083,686 6/1937 Campbell 92/168X 2,234,574 3/1941 Olcott 277/57 2,313,431 3/1943 G0epfrich.... 188/152X 2,405 ,093 7/1946 La Brie 92/168X 2,629,463 2/ 1953 Freeman 60/54.6X 2,712,367 7/1955 Schnell 188/152X 2,733,780 2/1956 Myers 60/54.6X 2,740,647 4/1956 Van Pelt..... 277/56X 3,127,181 3/1964 Crego et a1. 277/57X 3,144,280 8/1964 Sorenson.... 277/57X 3,177,984 4/1965 Taylor 92/168 3,336,842 8/1967 Adelt.

Primary Examiner-Martin P. Schwadron Assistant Examiner- Leslie J. Payne Att0mey-l(arl F. Ross ABSTRACT: A hydraulic cylinder whose piston is coupled ,struction and, more particularly, toimprovements in wheel brake cylinders for automotive vehicle internal-expansion or drum-type brakes.

It will be generally recognized that the hydraulic brake systems of automotive vehicles are merely special cases of hydraulic networks provided for the remote actuation of a rod under the control of a master hydraulic cylinder. The master cylinder, e.g. the brake pedal operated cylinder of an automotive vehicle, is connected to one or more slave or follower cylinders whose pistons, in turn, are operatively connected with the load, via suitable hydraulic transmission lines. In an automotive brake system, the load is a brake shoe which'is mounted upon a nonrotatable portion of the vehicle, e.g. a brake yoke or shield attached'to the axial housing, which is displaceable against a rotating surface connected with a vehicle wheel. Two broad types of wheel brakes may be considered, these types being designated respectively as disk brakes and drum brakes. While the present invention is described mainly in connection with the latter type of brake, it will be apparent that it may be equally applicable to the fonner and indeed to all systems in which the follower piston is connected to a load via a pressure transmitting member or rod.

In a drum-type or internal-expansion brake, a wheel brake cylinder is mounted upon thebrake shield and has one or two pistons which apply force 'outwardly to urge respective brakeshoes against the inner cylindrical surface of a drum. The brakeshoes, which conform to cylindrical segments, are juxtaposed with the drum at angularly spaced locations about the axis of rotation of the dfrumand are generally pivoted at one end of'the brakeshoe to 'the brake shield or a floating, force multiplying linkage connected in turn to the shield. At the other end of the brakeshoe, the respective wheel brake cylinder and piston deliver braking force via a pressure transmitting member or rod. The overall construction of a wheel brake of this type is described in;Principles of Automotive Vehicles", U.S. Govemment Printing Office, Washington DC. 1956. The brakeshoe generally has an arcuate backing plate, carrying a brake lining and reinforced by a spine or web extending perpendicularly to the backing plate and parallel to the brake shield upon which the cylinder is mounted. The pressure transmitting rod can thus have a notch receiving the spine to enable positive delivery of the actuating force to the brakeshoe.

In such systems, the hydraulic cylinder has as open end at which the forward face of the piston is exposedand through which the pressure transmitting rod extends. The forward face of the piston is commonly provided with a recess or socket having generally spheroidal bearing surfaces in which the complementarily shaped end of the pressure transmitting rod is received with some degree of swivel ability. The relative mobility of the rod and the piston is of advantage to permit thermal distortion changes of the various parts, to ensure displacement of the piston and rod without binding, and to permit at least some movement of the brakeshocs along with the disk as part of a self-tightening or force multiplying action. To prevent the passage of dust, moisture and other particulate and other contaminating materials in the region of the wheel brake cylinder combine to cause early deterioration of the cap and, upon such deterioration, the penetration of contaminants into the wheel brake cylinder.

It is, therefore, the principal object of the present invention to provide an improved wheel brake cylinder construction and dust cap assembly whereby the aforementioned disadvantages can be obviated and the penetration of liquid and dirt between the cylinder and the piston is precluded.

Another object of this invention is to provide an improved closure arrangement for an open end! of a hydraulic cylinder whereby the efiective temperature, oil and other contaminants, and relative movement of the several parts will not cause early deterioration of the seal.

We have found that it is possible to overcome completely all of the aforementioned disadvantages by providing, in a cylinder arrangement of the character described,,a metallic dust excluding cap which is generally cup shaped and has a mouth of substantially cylindrical configuration which fits slidablyover the open end of the wheel brake cylinder and is axially shiftable relatively thereto, the cap being made of drawn or spun metal without any perforation through which the rod may pass. Centrally of the cylindrical mouth of this cup, we form a craterl ike protuberance which extends axially into the cylinder beyond the axial limit of the cylindrical mouth and is complementarily received in thesocket of the piston, being held thereagainst by the correspondingly shaped pressure transmitting rod.

i The above and other objects, features and advantages of the FIG. 2 is a similar cross-sectional view illustrating another contaminants into the wheel brake cylinder, it has been the practice to provide the latter, apart from the seals between the piston and the cylinder wall, with a dust or contamination exeluding cap of elastomeric material and of annular (i.e. ringshaped) construction, the outer periphery ofthis cap being seated in a groove along the outer periphery of the cylinder, while the inner periphery engages the piston or the rod which, in either case, passes through the cap. The latter is composed of a rubberlike web which must flex or roll to permit movement of the force transmitting rod during brake operation. The movement, however, leads to stretching of the cap and eventually to a relaxationin the tightness with which the cap hugs the cylinder or rod. In addition, the friction of the aforementioned movements, the elevated temperature generated upon brake application and, frequently, the presence of oil embodiment thereof; and

FIG. 3 is a partial axially cross-sectional view of still another wheel brake cylinder.

In FIG. 1, we show a wheel brake cylinder for an internalexpansion brake, e.g. of the type described in the aforementioned publication, which comprises a cylinder housing 1 open at its opposite ends and receiving a pair of pistons one of which may be seen in section at 2. In FIG. 1 and in FIGS. 2 and 3, only a single piston assembly is shown although it will be understood that the other piston is symmetrically disposed on the other side of the cylinder. Between the pistons, the cylinder bore is formed with a working chamber 13 to which brake fluid is supplied from an inlet port 14. The cylinder 1 is sealed relative to the working chamber 13 by a rubber sealing cup 3 whose concavity, turned toward chamber 13, is filled with a block 4 against which a coil spring 15 bears so that the block 4 defines with the sealing cup 3,- an air reservoir 16. The stroke of the piston 2 is limited, atthe open side of cylinder 1, by a split ring 6 retained by its inherent resiliency in a groove 17.

In an outer peripheral groove ,18 adjacent the open end of the cylinder, a sealing ring 8 is seated for slidable engagement with a cylindrical apron 7a of a sheet metal dustcap 7. The dust cap is formed centrally with a craterlike protuberance 7b frustoconically converging inwardly along the axis of the cylinder and terminating beyond the: apron 7a in a generally spheroidal seat 70 complementarily to the seat 24 of the piston 2. The seat 2a diverges frustoconically from its spherical portion with an apex angleexceeding that of the frustoconical portion of the protuberance 7b. The: sheet metal dust cap 7, which can be drawn or spun from a metal disk and is unperforated, receives the force transmitting rod 5 whose spherical end is complementary to the spherical portion 7c of the dust cap. Rod 5 has a split end 5a which engages the spine of the corresponding brakeshoeand retains the'dust' cap 7 in the socket 2a. The dust cap v7 is axiallyshiftable (arrow A) with the piston 2 and the rod 5 to-prevent entry of the dirt, dust and other contaminants (cg. moisture), into the cylinder. The rounded head of the rod 5 is tightly hugged by the spherical portion 70 of the cap, thereby ensuring a rigid connection of the three elements 2, 5, and 7. The seal 8 slidably engages the inner'wall of the apron 7a to further ensure a satisfactory seal.

In the system of FIG. 2, the cylinder 21 cooperates with a piston 22 whose cup 23 and filler body 24 have been previously described. In this embodiment, however, instead of the seal 8, a labyrinth arrangement is provided by a sheet metal shell 29 which is force-fitted to a boss 21 formed peripherally on the cylinder 21 at a location axially inwardly of the mouth. The split ring 26 forms a stop of the piston 22. The shell 29 has a inwardly turned lip 29a and defines with the periphery of the cylinder 21, and axially extending annular compartment 29b into which the cylindrical apron 27a of the sheet metal dust cap 27 extends. In this embodiment as well, the frustoconical protuberance 27b terminates in a spherical socket 270 for the rounded end of the pressure transmitting rod 25 and is held by this rod in the socket 22a in the forward end of the piston 2. The labyrinth seal permits axial displacement of the dust cap without slidable engagement of a sealing ring therewith.

In the modification of FIG. 3, the cylindrical seal 30, mounted upon a shoulder 31' of the cylinder 31 is formed close to the mouth of the cylinder with an annular groove 41 bent integrally from the sheet metal and receiving a circular cross section sealing ring 42 (i.e. an'O-ring) which bears upon the outer periphery of the cylindrical apron 27a of the sheet metal dust cap 37. In this embodiment as well, the protuberance 37b of the apron is retained in the socket 32a of the piston 32 by the pressure transmitting rod 35 while the piston has a sealing cup 33 against which the filler body 34 acts. The split ring 36 limits the stroke of piston 32.

We claim:

1. A wheel brake cylinder of an automotive vehicle brake system assembly adapted to receive a hydraulic fluid and capable of operating a brakeshoe of said system, comprising:

housing means forming a cylinder open at one end;

a piston axially shiftable in said cylinder and formed with a rounded socket facing in the direction of said end;

a sheet metal dust cap axially shiftable relatively to said cylinder and substantially closing said end of said cylinder, said dust cap having an inwardly converging frustoconical protuberance extending within said cylinder and complementarily received in said socket, and a generally cylindrical apron surrounding said housing means in the region of the open end of said cylinder and constituting one piece with said protuberance;

a pressure transmitting rod having a generally spherically rounded extremity received in said protuberance for retaining same in said socket, retaining said cap against said piston and operatively connected with said brakeshoe; and

sealing means on said housing means in the region of said open end and cooperating with said apron to restrict entry of contaminants into said cylinder through said open end.

2. The assembly defined in claim 1 wherein said sealing means includes an annular seal slidably engaging said apron.

3. A wheel brake cylinder of an automotivevehicle brake system assembly adapted to receive a hydraulic fluid and capable of operating a brakeshoe of said system, comprising:

housing means forming a cylinder open at one end;

a piston axially shiftable in said cylinder and formed with a rounded socket facing in the direction of said end;

a sheet metal dust cap axially shiftable relatively to said cylinder and substantially closing said end of said cylinder, said dust cap having an inwardly converging frustoconical protuberance extending-within said cylinder and complementarily received in said socket, and a generally cylindrical apron surrounding said housing means in the region of the open end of said cylinder and constituting one piece with said protuberance;

a pressure transmitting rod having a generally spherically rounded extremity received in said protuberance for retaining same in said socket retaining said cap against said piston and operatively connected with said brakeshoe; and

sealing means on said housing means in the region of said open end and cooperating with said apron to restrict entry of contaminants into said cylinder through said open end, said sealing means including an annular seal slidably engaging the outer periphery of said apron.

4. A wheel brake cylinder of an automotive vehicle brake system assembly adapted to receive a hydraulic fluid and capable of operating a brakeshoe of said system, comprising:

housing means forming a cylinder open at one end;

a piston axially shiftable in said cylinder and formed with a rounded socket facing in the direction of said end;

a sheet metal dust cap axially shiftable relatively to said cylinder and substantially closing said end of said cylinder, said dust cap having an inwardly converging frustoconical protuberance extending within said cylinder and complementarily received in said socket, and a generally cylindrical apron surrounding said housing means in the region of the open end of said cylinder and constituting one piece with said protuberance;

a pressure transmitting rod having a generally spherically rounded extremity received in said protuberance for retaining same in said socket, retaining said cap against said piston and operatively connected with said brakeshoe; and

sealing means on said housing means in the'region of said open end and cooperating with said apron to restrict entry of contaminants into said cylinder through said open end, said sealing means including a cylindrical shell mounted upon said housing means and surrounding said apron while defining therewith a labyrinth-type seal.

5. The assembly defined in claim 4, further comprising a sealing ring mounted on said shell and slidably engaging said apron.

6. The assembly defined in claim 5, wherein said seal engages the inner periphery of said apron. 

